The transient processes in multi-pulse nitrogen-14 NQR

It has been demonstrated that transient processes, observed in a single crystal of NaNO₂ acted upon by pulse sequences MW-2 and MW-4 and their modifications with 180° flip angle of the pulses (Solid State Nucl. Magn. Resonance 10 (1997) 63; Sov. Phys.—JETP 88(5) (1999) 1580), which manifest themselves in the oscillating form of the NQR signals envelope, can be explained in the frames of a two-particle model. It has been proved that the nature of echo signals in the effective field of multi-pulse sequences received by the inversion of the phase of the sequence pulses or by introducing an additional 180° pulse is connected with re-focusing of accumulated digressions of the flip angle from the ideal 180° pulse. Experimental results of observing single and multiple echoes in a number of powdered nitrogenated substances in the effective field of various sequences at room temperature have been presented.